docs: def diffplot(self, f, delay=1, lfilter=None, **kargs):
          """diffplot(f, delay=1, lfilter=None)
          Applies a function to couples (l[i],l[i+delay])"""
  
          return plt.plot([ f(i, j) for i in self.res[:-delay] for j in self.res[delay:] if not lfilter or (lfilter(i) and lfilter(j))], 
              **kargs)